Xerographic processes for producing a permanent image on plain paper are well known and commonly used in office copiers, laser printers and microfilm reader/printers. In general, these processes all include: (1) charging a photoreceptor which is a roll or continuous belt bearing a photoconductor material; (2) exposing the charged area to a light image to produce an electrostatic charge on the area in the shape of the image; (3) presenting developer particles to the photoreceptor surface bearing the image so that the particles are transferred to the surface in the shape of the image; (4) transferring the particles in the shape of the image from the photoreceptor to the paper; (5) fusing or fixing the particles in the shape of the image to the paper; and (6) cleaning or restoring the photoreceptor for the next printing cycle. Further information about xerographic processes is available in the text "The Physics and Technology of Xerographic Processes", by Edgar M. Williams, 1984, A Wiley-Interscience Publication of John Wiley & Sons, the disclosure of which is hereby incorporated by reference.
In virtually all of these processes, it is important that the developer particles be presented to the photoreceptor in a layer of uniform thickness and uniform electrostatic charge. If the particles are not properly charged, control of the transfer of the particles to the electrostatic image bearing areas of the photoreceptor becomes exceedingly difficult and particles will migrate to the non-image or "white" areas of the photoreceptor. Moreover, if the thickness of the layer as presented to the photoreceptor is not uniform, more or less developer particles will be presented to the photoreceptor, ultimately resulting in darker or lighter areas of printing on the final copy.
Most prior developer dispensers use a roll or other continuous conveyor (e.g., a continuous belt) to transfer developer particles, which may be either two component or monocomponent, from a reservoir of developer particles past a regulating gap which is established by a "doctor blade". Stationary magnets are usually provided inside the conveyor to produce a force of attraction of the developer particles against the surface of the conveyor. As the surface of the conveyor is rotated past the doctor blade, the size of the gap determines the thickness of the developer layer formed on the surface of the conveyor and presented to the photoreceptor.
The developer particles are formulated to acquire either a positive or a negative electrostatic charge. For this charging to take place, however, the particles must be rubbed against the surface of the conveyor or against a dissimilar material so that triboelectrification, also known as contact or frictional electrification, takes place. This charging takes place primarily from the contact which occurs as the developer particles are metered through the regulating gap as they come into contact with and slide over the surface of the developer conveyor.
If the regulating gap in monocomponent systems is too large, only the innermost layer of developer particles which contacts the surface of the conveyor may become electrostatically charged. The outer layer, which does not come into significant contact with the surface of the conveyor may not become electrostatically charged, but may remain randomly charged. The result is that the randomly charged particles may be attracted to the non-image bearing portions of the photoreceptor, resulting in a poor quality copy.
The gap established by the doctor blade in prior art dispensers of monocomponent developer has commonly been approximately 0.003-0.005 inches. This gap has been necessary in such dispensers to insure that the developer particles passing through the gap become properly electrostatically charged. It has also generally been necessary to hold the doctor blade to within 0.001 inches of being parallel to the developer conveyor to insure that the thickness of the developer particle layer formed on the surface of the conveyor is adequately uniform. These small tolerances have required high precision components resulting in correspondingly high manufacturing costs.
Efforts have been made to make the doctor blade out of iron or other magnetic material so as to allow the regulating gap established by the doctor blade to be somewhat greater. While these efforts have resulted in some widening of the gap, the gap is still relatively critical and the components must still be manufactured to precise tolerances.
Where the developer conveyor comes in close proximity to the photoreceptor, the developer is transferred to the electrostatic image (also known as the latent image) on the photoreceptor, thereby making the image visible. The visual image is usually then transferred to a sheet of paper. However, some of the developer may remain on the photoreceptor, which must be removed prior to the next electrostatic image being formed on the photoreceptor. Typically, the remaining developer is removed by being scraped off and may be discarded, or can be recycled by returning the scraped off material to the developer reservoir.
When the developer is scraped off of the photoreceptor and recycled, a problem can arise that contaminants, such as paper fibers, are also scraped off with the developer particles and returned to the developer reservoir. The contaminant particles can be many times larger than the developer particles and can be larger than the gap formed by the doctor blade. When such contaminants enter the regulating gap, they can obstruct the passage of developer past the gap and cause areas on the developer conveyor which are void of developer particles. For example, if a contaminant particle gets caught between the doctor blade and the conveyor, a bare track may result around the conveyor. Accordingly, when these void areas reach the development region, the latent image on the photoreceptor corresponding to those void areas does not receive developer particles in a sufficient quantity and therefore is not properly developed.
In addition, another problem has arisen in refilling developer dispensers. Developer particles, because of their small size, light weight, and typically dark color, are extremely messy to handle. Prior techniques are known for refilling dispensers with developer particles, but suffer to varying degrees of being messy, inconvenient to handle, or expensive to implement. Therefore, a need also exists for an improved means for refilling a developer dispenser with developer particles.